Technical Field
The present invention relates to a method for displaying a video stream, and in particular to a method for allowing a user to define a customised display format which can be recalled manually by the user or automatically by the device displaying the video stream.
Prior Art
In developed countries, television sets, monitors and other types of video screens have now undergone the transition from the 4:3 aspect ratio to the “Widescreen” 16:9 aspect ratio for video stream display.
The term “aspect ratio” refers to the mathematical ratio between frame width and frame height in a video stream.
Although most latest-generation displays have been optimised for 16:9 video contents, there are still television programs with different original aspect ratios, even within the same broadcast. This requires that the most appropriate display format be selected in order to make the program more pleasant for the spectator. For example, sometimes one television broadcaster broadcasts programs in the 4:3 format and other programs in the 16:9 format, depending on their native (i.e. recording) format. Other times, broadcasters frame the image of the original video stream (e.g. a film recorded in any one of the various aspect ratios, such as 2.35:1, 1.85:1 or 1.78:1) by adding black-background bands (called mattes) above and under the original image.
These mattes (which may be arranged on one or more sides to frame the original image) are often used for advertising or information purposes by television broadcasters, who enter into them texts, images, logos or other accessory contents, whether or not related to the content of the original video stream and often representing a sort of frame for the main image.
These bands, especially when they contain advertisements or other auxiliary dynamic contents, occupy a large portion of the space available on the television screen, and may therefore be annoying for the spectator, who is generally more interested in the image comprised in between these bands.
In order to adapt the visualisation of video contents to the screen size, devices are known at present which can recognise the format of the video stream being broadcast based on information contained in the television signal (e.g. in “Wide Screen Signaling” (WSS) for analog broadcasting or in the tables of the “transport stream” or in the “sequence header” for digital broadcasting), so that they can adapt the display mode to the screen size.
However, these devices are only effective for areas containing no visual information, and cannot take into account any bands introduced at video production level. Furthermore, their operation is heavily dependent on the accuracy of the information about the format of the video stream contained in the video signal itself; if such information is incorrect or is not updated by the television broadcaster, the device will not operate correctly.
Devices are also known which allow the display mode of the video stream (broadcast by a television broadcaster or played from a storage medium) to be manually adjusted in accordance with factory settings predefined by the device manufacturer. The user will select a display format among the predefined formats available in the device (for example: “4:3”, “16:9”, “Widescreen”, “Central zoom”, “Cinema”, etc.), and then the device will execute image resizing, cutting or deformation operations on the received video stream according to the option chosen by the user.
However, since spectators have different tastes, the resizing options set at the factory cannot cover the preferences of all users. In order to meet this requirement, the Samsung LE 40A856S1M television set allows to select a user-defined “customised” display mode called “ZOOM” by means of a special configuration procedure, which is however time-consuming, complex and not very intuitive. In order to define the display mode, in fact, the user must interact several times with the television set by moving and expanding the image without having a complete vision of the full image.
Finally, there are automatic resizing methods wherein the device directly analyses the active content of the video stream and autonomously changes the display mode on the basis of such content, thereby resizing it; a device of this type is known, for example, from patent EP0685139.
However, the results obtained from these methods are not always satisfactory for the user: the algorithm for automatically detecting the active areas of the video stream cannot correctly detect and identify any areas containing information of interest for the user, since it is exclusively based on the luminance threshold of the pixels of each frame of the video stream. Since the frames of the video stream may vary considerably their content instant by instant (e.g. during advertising breaks or if the displayed program is changed), the device may execute an annoying and disturbing series of useless successive resizing operations which will ruin the visual experience.